SUMMARY OF INVESTMENTS (Fair Value of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
HELD-TO-MATURITY
Cost or Amortized Cost	$ 672	$ 397
Held-to-maturity securities	675	404
AVAILABLE-FOR-SALE
Cost or Amortized Cost	2,861,583	2,845,217
Gross Unrealized Appreciation	227,716	257,633
Gross Unrealized Depreciation	28,091	13,928
Fair Value	3,061,208	3,088,922
Fixed Maturities [Member]
HELD-TO-MATURITY
Cost or Amortized Cost	672	397
Gross Unrealized Appreciation	3	7
Gross Unrealized Depreciation	0	0
Held-to-maturity securities	675	404
AVAILABLE-FOR-SALE
Cost or Amortized Cost	2,793,069	2,773,566
Gross Unrealized Appreciation	58,994	82,882
Gross Unrealized Depreciation	27,102	13,369
Fair Value	2,824,961	2,843,079
U.S. Treasury [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	21,587	25,856
Gross Unrealized Appreciation	100	168
Gross Unrealized Depreciation	38	52
Fair Value	21,649	25,972
U.S. Government Agency [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	232,808	349,747
Gross Unrealized Appreciation	2,622	4,347
Gross Unrealized Depreciation	2,400	2,422
Fair Value	233,030	351,672
General Obligations [Member] | Midwest [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	160,484	179,491
Gross Unrealized Appreciation	4,990	6,599
Gross Unrealized Depreciation	18	170
Fair Value	165,456	185,920
General Obligations [Member] | Northeast [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	56,449	59,084
Gross Unrealized Appreciation	1,996	2,120
Gross Unrealized Depreciation	0	50
Fair Value	58,445	61,154
General Obligations [Member] | South [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	125,565	122,055
Gross Unrealized Appreciation	3,358	4,453
Gross Unrealized Depreciation	134	288
Fair Value	128,789	126,220
General Obligations [Member] | West [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	103,721	75,102
Gross Unrealized Appreciation	3,160	3,350
Gross Unrealized Depreciation	67	19
Fair Value	106,814	78,433
Special Revenue [Member] | Midwest [Member]
HELD-TO-MATURITY
Cost or Amortized Cost		55
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Held-to-maturity securities		55
AVAILABLE-FOR-SALE
Cost or Amortized Cost	152,780	126,192
Gross Unrealized Appreciation	4,956	5,356
Gross Unrealized Depreciation	30	146
Fair Value	157,706	131,402
Special Revenue [Member] | Northeast [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	23,892	11,767
Gross Unrealized Appreciation	919	864
Gross Unrealized Depreciation	212	0
Fair Value	24,599	12,631
Special Revenue [Member] | South [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	144,183	106,917
Gross Unrealized Appreciation	4,281	4,368
Gross Unrealized Depreciation	27	63
Fair Value	148,437	111,222
Special Revenue [Member] | West [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	78,935	68,024
Gross Unrealized Appreciation	3,150	3,285
Gross Unrealized Depreciation	44	6
Fair Value	82,041	71,303
Foreign Bonds [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	82,580	136,487
Gross Unrealized Appreciation	2,405	4,132
Gross Unrealized Depreciation	2,457	446
Fair Value	82,528	140,173
Public Utilities [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	213,233	206,366
Gross Unrealized Appreciation	3,701	6,479
Gross Unrealized Depreciation	1,251	488
Fair Value	215,683	212,357
Corporate Bonds [Member]
HELD-TO-MATURITY
Cost or Amortized Cost		200
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Held-to-maturity securities		200
Corporate Bonds [Member] | Energy [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	116,800	135,068
Gross Unrealized Appreciation	1,032	2,858
Gross Unrealized Depreciation	4,713	793
Fair Value	113,119	137,133
Corporate Bonds [Member] | Industrials [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	227,589	211,256
Gross Unrealized Appreciation	3,329	6,373
Gross Unrealized Depreciation	6,663	2,154
Fair Value	224,255	215,475
Corporate Bonds [Member] | Consumer Goods and Services [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	172,529	172,623
Gross Unrealized Appreciation	2,844	4,702
Gross Unrealized Depreciation	776	324
Fair Value	174,597	177,001
Corporate Bonds [Member] | Health Care [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	92,132	86,017
Gross Unrealized Appreciation	2,168	3,228
Gross Unrealized Depreciation	791	210
Fair Value	93,509	89,035
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
HELD-TO-MATURITY
Cost or Amortized Cost	450
Gross Unrealized Appreciation	1
Gross Unrealized Depreciation	0
Held-to-maturity securities	451
AVAILABLE-FOR-SALE
Cost or Amortized Cost	142,431	131,465
Gross Unrealized Appreciation	1,972	3,863
Gross Unrealized Depreciation	2,003	799
Fair Value	142,400	134,529
Corporate Bonds [Member] | Financial Services [Member]
HELD-TO-MATURITY
Cost or Amortized Cost	150
Gross Unrealized Appreciation	0
Gross Unrealized Depreciation	0
Held-to-maturity securities	150
AVAILABLE-FOR-SALE
Cost or Amortized Cost	259,382	215,095
Gross Unrealized Appreciation	5,246	8,574
Gross Unrealized Depreciation	1,143	87
Fair Value	263,485	223,582
Mortgage-Backed Securities [Member]
HELD-TO-MATURITY
Cost or Amortized Cost	72	142
Gross Unrealized Appreciation	2	7
Gross Unrealized Depreciation	0	0
Held-to-maturity securities	74	149
AVAILABLE-FOR-SALE
Cost or Amortized Cost	16,413	17,121
Gross Unrealized Appreciation	376	483
Gross Unrealized Depreciation	51	46
Fair Value	16,738	17,558
Collateralized Mortgage Obligations [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	364,115	335,092
Gross Unrealized Appreciation	6,168	7,003
Gross Unrealized Depreciation	4,268	4,806
Fair Value	366,015	337,289
Asset-backed Securities [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	5,461	2,741
Gross Unrealized Appreciation	221	277
Gross Unrealized Depreciation	16	0
Fair Value	5,666	3,018
Equity Securities [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	68,514	71,651
Gross Unrealized Appreciation	168,722	174,751
Gross Unrealized Depreciation	989	559
Fair Value	236,247	245,843
Common Stock [Member] | Public Utilities [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	7,231	7,231
Gross Unrealized Appreciation	12,022	13,103
Gross Unrealized Depreciation	193	44
Fair Value	19,060	20,290
Common Stock [Member] | Energy [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	6,103	5,094
Gross Unrealized Appreciation	5,374	8,623
Gross Unrealized Depreciation	266	0
Fair Value	11,211	13,717
Common Stock [Member] | Industrials [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	13,251	13,284
Gross Unrealized Appreciation	31,872	32,299
Gross Unrealized Depreciation	313	124
Fair Value	44,810	45,459
Common Stock [Member] | Consumer Goods and Services [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	10,301	10,294
Gross Unrealized Appreciation	13,017	13,295
Gross Unrealized Depreciation	3	275
Fair Value	23,315	23,314
Common Stock [Member] | Health Care [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	7,763	7,920
Gross Unrealized Appreciation	20,454	22,436
Gross Unrealized Depreciation	0	0
Fair Value	28,217	30,356
Common Stock [Member] | Technology, Media and Telecommunications [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	5,931	6,207
Gross Unrealized Appreciation	7,538	7,846
Gross Unrealized Depreciation	105	58
Fair Value	13,364	13,995
Common Stock [Member] | Financial Services [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	17,392	16,637
Gross Unrealized Appreciation	78,411	77,077
Gross Unrealized Depreciation	109	51
Fair Value	95,694	93,663
Nonredeemable Preferred Stocks [Member]
AVAILABLE-FOR-SALE
Cost or Amortized Cost	542	4,984
Gross Unrealized Appreciation	34	72
Gross Unrealized Depreciation	0	7
Fair Value	$ 576	$ 5,049